This invention relates to follower plates used in dispensing apparatus, and more particularly, to integrally fabricated heater follower plates used in hot melt dispensing apparatus. Two embodiments of such integrally fabricated heater follower plates used with specific hot melt dispensing apparatus are disclosed in copending U.S. application Ser. No. 633,649, filed Nov. 20, 1975.
In recent years, various different materials that are now commonly called hot melt materials have been developed. These materials which are either unpumpable solids or high viscosity unpumpable liquids at or below a given temperature, becomes less viscous pumpable liquids when heated to or above a given temperature. There are many different types of hot-melt materials and these various different hot melt materials require different temperatures to convert them from a solid to a pumpable liquid or from a highly viscous unpumpable liquid to a less viscous pumpable liquid.
Several different types of dispensers have been developed for heating and dispensing hot melt materials from their containers and many of these dispensers available on the market utilize a follower plate in combination with a heater. The follower plate and the heater are generally lowered into the container that contains the hot melt material. The heater is then energized to melt the hot melt material. As the hot melt material is melted, it is removed from its container generally by means of a pump that pumps the hot melt material out of the container usually through an opening provided in the follower plate. As the material is dispensed from its container, the heater and the follower plate move down into the container thereby continuously melting the material so that it can be pumped out of its container.
To Applicant's knowledge, except for the integrally fabricated heater follower plates disclosed in his aforesaid copending application, the prior art heater and follower plates are two separate structural elements or plates. For example, the apparatus disclosed in U.S. Pat. No. 3,282,469 to Shonberg includes a follower plate and a separate heated plate that is located below the follower plate and the apparatus disclosed in U.S. Pat. No. 3,412,903 includes a follower plate and a separate heater plate located below and spaced apart from the follower plate. In the apparatus disclosed in both of the aforementioned U.S. patents, the heater plate is located below the follower plate. In the aforesaid U.S. Pat. No. 3,282,469, the heater plate is secured to the bottom of the follower plate, while in the aforesaid U.S. Pat. No. 3,412,903 the heater plate is suspended from the bottom of the follower plate. Thus, in both of these U.S. patents, the heater and follower plate are separate elements. In use the heater plate and the follower plate of the two aforementioned U.S. patents and in most, if not all, prior art hot melt dispensers using follower and heater plates, the follower plate and heater plate are lowered into the container, usually a drum, that contains the hot melt material. Therefore, if the heater malfunctions or burns out while in use, the entire assembly must be removed from the container in order to repair or replace the heater. Of course, while the heater plate and follower plate are removed to repair or replace the heater plate the dispensing apparatus has to be taken off-line. This can be a time consuming and thus costly process.
The heater follower plates of this invention are fabricated as an integral unit. That is, there is no separate heater plate utilized in the integral-heater follower plates of this invention; instead, the heater of the integral heater follower plates of this invention is integrated into the follower plate. In the first of two basic embodiments of this invention the heater comprises at least one spiral heating element that is embedded into one surface of the follower plate and in the second of the two basic embodiments of this invention the heater is made up of a plurality of individual cartridge heaters located in holes cut into the follower plate. In the first of the two basic embodiments of this invention, the follower plate must be removed from the container to repair the heater, which as mentioned is the case with the prior art heater plate and follower plate combinations; however, in the second of the two basic embodiments of this invention, the cartridge heaters can be individually removed and replaced without removing the follower plate from the container. Thus, this invention not only provides an integral heater follower plate but also provides in one of the two basic embodiments disclosed an integral heater follower plate in which the heater can be repaired without removing the apparatus from the container which contains the hot melt material.